1. Field of the Invention
The present invention relates to a visual axis detection apparatus used for a film, a camera, a video camera, a still video camera, an observation equipment, or the like, and also, to an optical apparatus provided therewith.
2. Related Background Art
There has hitherto been known a camera provided with a visual axis detection means which is mounted in a part of the camera for detecting the visual axis direction of a photographer for the detection of an area (position) where the photographer is observing in the finder field, the so-called photographer's target direction, and then, the various photographing functions, such as an automatic focus adjustment, an automatic exposure, are controlled among others in accordance with signals from the visual axis detection means thus arranged.
In this respect, the so-called visual axis detection apparatus with which to detect the position being observed by an observer on the observation plane of an optical apparatus disclosed in Japanese Patent Laid-Open Application No. 61-61135, Japanese Patent Laid-Open Application No. 61-172552, Japanese Patent Laid-Open Application No. 1-241511, and Japanese Patent Laid-Open Application No. 2-5 among some others.
In the Japanese Patent Laid-Open Application No. 61-61135, for example, a camera is disclosed, in which the distance measuring direction of a focal point detection apparatus is controlled by the output from a visual axis detection means in order to adjust the state of the focal point in the photographing system.
Also, in a specific example disclosed in the Japanese Patent Laid-Open Application No. 1-241511, there is proposed a camera comprising visual axis detection means for detecting the photographer's target direction, focal point detection means having a plurality of distance measuring fields, and automatic exposure control means having a plurality of photometric sensitivity distributions, thus controlling the driving of the focal point detection means, and then, the automatic exposure control means in accordance with the output of the visual axis detection means.
For the auto-focus operation provided for a camera, it has hitherto been in practice that a focal point detection is executed until a photographing lens is brought in the in-focus state, and then, after the lens is once in the in-focus state, there are two operations to follow, that is, one-shot operation which does not require any focal point detection, and a servo operation which continues the execution of the focal point detection irrespective of the in-focus state of the photographing lens.
The one-shot operation is a mode mainly used when an object does not move.
The operation of the one-shot mode of an auto-focus camera having an incorporated visual axis detection apparatus is executed in the following manner.
At first, a release switch is slightly depressed to turn on a switch SW1. Then, before any focal point detection, the photographer's target point in the finder is obtained by use of the visual axis detection apparatus. In this procedure, the sensor accumulation is executed for the visual axis detection means which comprises a CCD line sensor and the like in order to read out image signals. Based upon such image signals, the visual axis direction of the photographer is obtained.
Subsequently, from the visual axis direction thus obtained, the part to which the photographer's attention is directed in the finder, that is, the photographer's target point is calculated. This target point is represented by the coordinates in the finder.
Hence, this method is to determine the corresponding measuring distance point from the coordinates in the finder.
In this way, the against measuring distance point obtained by use of the visual axis detection means, the focal point detection apparatus detects the state of the focal point detection. On the basis of such information, the photographing lens is driven until it is brought in the in-focus state. Once the measuring distance point is determined by use of the visual axis detection apparatus, the focusing operation will be executed until coming into focus by merely giving attention to the in-focus state at such measuring distance point.
Now, the servo operation is a mode mainly used while an object is moving.
The operation is executed in the following manner for the servo mode of an auto-focus camera having a conventional visual axis detection apparatus.
In the same way as the one-shot operation, the measuring distance point is determined by use of the visual axis detection means immediately after the switch SW1 is turned on. On the basis of the information obtained by the focal point detecting operation for such measuring distance point, the lens is driven, and then, the operation will continue.
However, since the object is apt to move when the servo mode is executed, there are some cases where the object may be out of the measuring distance point thus obtained. Also, in the servo mode, it is occasionally desired that the related composition should be modified while bringing the object in focus.
In order to attain this aim, the photographer's target point should be extracted at certain intervals. By each interval it is extracted, the focal point state in the related area must be detected so that the photographing lens is driven on the basis of such an information. Nevertheless, to obtain a desirable precision, there are many numbers of pixels in the sensor which are needed for the detection of the light intensity distribution in the two-dimensional directions in order to photodetect the image of the photographer's eyeball. Inevitably, therefore, it takes an extremely long time to execute the required reading and processing operations.
As a result, the processing cycle becomes longer due to the long time required for the execution of the visual axis detection operation, hence presenting a problem that the servo AF (Auto Focus) responsibility is lowered, and that the speed with which to feed the frames is slower in taking pictures in continuation.
Also, in a visual axis detection apparatus specifically exemplified in Japanese Patent Laid-Open Application No. 4-347128 (corresponding to Japanese Patent Application No. 3-121092), not all the pieces of image information are stored in a memory at once, but stored in it sequentially while reading the photoelectric signals which are being output from the sensor in time series. The reading is once paused for processing when the information is secured in an amount which is good enough for the current execution. Then, the processed image information is not held in the memory as it is, but new photoelectric conversion signals will be stored. In this way, even in a case where only a limited capacity of memory is usable, it is possible to process all the information available.
Now, when the visual axis direction is detected by processing the image signals from the area sensor comprising a plurality of the photoelectric conversion element arrays, there is a problem that it takes an enormous amount of time if the characteristic points of image (minimum luminance sections, pupil's edge, and Purkinje images, for example) are to be detected over the entire sensor area because of the extremely great number of the photoelectric conversion elements (pixels).